Fair Value (The Fair Value Calculated Using An Industry Accepted Option Pricing Model, Black-Scholes) (Details)	Dec. 31, 2011
FTSE 100 Index [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity index	5,572.3
Interest rate	3.76%
Time to maturity, years	8.6
Volatility	24.70%
Standard & Poor's 500 Index [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity index	1,257.6
Interest rate, range minimum	3.09%
Interest rate, range maximum	4.37%
Time to maturity, range minimum, years	5.4
Time to maturity, range maximum, years	19.3
Volatility, minimum	22.40%
Volatility, maximum	25.10%